Beam-off motion thresholds in radiation therapy based on breath-hold level determination

ABSTRACT

A computer-implemented method of performing a treatment fraction of radiation therapy comprises: determining a current position of a target volume of patient anatomy; based on the current position of the target volume, computing an accumulated dose for non-target tissue proximate the target volume; determining that the accumulated dose is less than a current value for a dose budget of the non-target tissue; and in response to the accumulated dose being less than the current value for the dose budget, applying a treatment beam to the target volume while the target volume is in the current position.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation under 35 U.S.C. § 120 of U.S.Pat. No. 17,138,856, filed Dec. 30, 2020. The aforementioned U.S. patentapplication is incorporated herein by reference.

BACKGROUND

Unless otherwise indicated herein, the approaches described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Radiation therapy is a localized treatment for a specific target tissue(a planning target volume), such as a cancerous tumor. Ideally,radiation therapy is performed on the planning target volume that sparesthe surrounding normal tissue from receiving doses above specifiedtolerances, thereby minimizing risk of damage to healthy tissue. Priorto the delivery of radiation therapy, an imaging system is typicallyemployed to provide a three-dimensional image of the target tissue andsurrounding area. From such imaging, the size and mass of the targettissue can be estimated, a planning target volume determined, and anappropriate treatment plan generated.

So that the prescribed dose is correctly supplied to the planning targetvolume (i.e., the target tissue) during radiation therapy, the patientshould be correctly positioned relative to the linear accelerator thatprovides the radiation therapy. Typically, dosimetric and geometric dataare checked before and during the treatment, to ensure correct patientplacement and that the administered radiotherapy treatment matches thepreviously planned treatment. This process is referred to as imageguided radiation therapy (IGRT), and involves the use of an imagingsystem to view target tissues immediately before or while radiationtreatment is delivered to the planning target volume. IGRT incorporatesimaging coordinates from the treatment plan to ensure the patient isproperly aligned for treatment in the radiation therapy device.

SUMMARY

In accordance with at least some embodiments of the present disclosure,a method of breath-hold-based radiation therapy is disclosed thatemploys beam-off thresholds for allowable movement of a target region(or volume) of patient anatomy relative to a planned treatment locationfor the target volume. The beam-off thresholds are based on one or moredosimetrically determined treatment breath-hold levels for a particularpatient. In some embodiments, a treatment breath-hold level for theparticular patient is determined based on imaging of the target volumeat multiple breath-hold levels, a treatment plan for the treatmentbreath-hold level is generated, and the beam-off thresholds aredetermined based on dosing information that is calculated using imageinformation for one or more breath-hold levels that are proximate to thetreatment breath-hold level. In some embodiments, breath-hold level ofthe patient is monitored during treatment based on an external breathingsignal (measured using a fiducial or other external marker, forexample), X-ray imaging of the target volume, or a combination of both.Further, in some embodiments, dynamic beam-off thresholds are employedthat are modified during a treatment fraction based on dose acquired innon-target tissue during the treatment fraction.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. These drawingsdepict only several embodiments in accordance with the disclosure andare, therefore, not to be considered limiting of its scope. Thedisclosure will be described with additional specificity and detailthrough use of the accompanying drawings.

FIG. 1 is a perspective view of a radiation therapy system that canbeneficially implement various aspects of the present disclosure.

FIG. 2 schematically illustrates a drive stand and gantry of theradiation therapy system of FIG. 1 , according to various embodiments.

FIG. 3 schematically illustrates a drive stand and a gantry of theradiation therapy system of FIG. 1 , according to various embodiments.

FIG. 4 schematically illustrates a digital volume that is constructedbased on projection images generated by one or more X-ray imagesincluded in the radiation therapy system of FIG. 1 , according tovarious embodiments.

FIG. 5 is a block diagram illustrating a breath-hold-based radiationtherapy process, according to various embodiments.

FIG. 6 sets forth a flowchart of the dosimetric analysis phase of FIG. 5, according to one or more embodiments.

FIG. 7 is an illustration of a breath-hold curve, according to variousembodiments.

FIG. 8 is an illustration of a breath-hold correlation curve, accordingto various embodiments.

FIG. 9 is an illustration of a breath-hold correlation curve with staticbeam-off thresholds, according to various embodiments.

FIG. 10 is an illustration of a breath-hold correlation curve withdynamic beam-off thresholds, according to various embodiments.

FIG. 11 sets forth a flowchart of a treatment fraction process of theradiation therapy phase of FIG. 5 , according to one or moreembodiments.

FIG. 12 is an illustration of a computing device configured to performvarious embodiments of the present disclosure.

FIG. 13 is a block diagram of an illustrative embodiment of a computerprogram product for implementing one or more embodiments of the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here. It will be readily understood that the aspects of thedisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, and designed in a widevariety of different configurations, all of which are explicitlycontemplated and make part of this disclosure.

Image guided radiation therapy (IGRT) is used to treat tumors in areasof the body that are subject to voluntary movement, such as the lungs,or involuntary movement, such as organs affected by peristalsis, gasmotion, muscle contraction and the like. IGRT involves the use of animaging system to view target tissues (also referred to as the “targetvolume”) immediately before or while radiation treatment is deliveredthereto. In IGRT, image-based coordinates of the target volume from apreviously determined treatment plan are compared to image-basedcoordinates of the target volume determined immediately before or duringthe application of the treatment beam. In this way, changes in thesurrounding organs at risk and/or motion or deformation of the targetvolume relative to the radiation therapy system can be detected.Consequently, dose limits to organs at risk are accurately enforcedbased on the daily position and shape, and the patient's position and/orthe treatment beam can be adjusted to more precisely target theradiation dose to the tumor. For example, in pancreatic tumortreatments, organs at risk include the duodenum and stomach. The shapeand relative position of these organs at risk with respect to the targetvolume can vary significantly from day-to-day. Thus, accurate adaptionto the shape and relative position of such organs at risk enablesescalation of the dose to the target volume and better therapeuticresults.

In some radiation therapy systems, breath-hold-based radiation therapyis performed, in which the patient performs one or more breath holdsthroughout the treatment fraction. Breath-hold-based radiation therapyis often employed to separate an organ at risk or other criticalanatomical structure from the target volume during the beam delivery ofthe treatment fraction. In addition, breath-hold-based radiation therapycan reduce the motion and/or deformation of a target volume caused bypatient respiration, thereby reducing the dose received by non-targettissue. However, maintaining a breath hold for the time intervalsassociated with radiation therapy can be challenging for many patients,and significant motion of a target volume can occur due to involuntaryloss of the breath hold during breath-hold-based radiation treatment.Further, no patient can maintain a perfectly motionless breath hold and,as a result, at least some motion of a target volume typically occursthroughout a breath hold.

In conventional radiation therapy systems, when the detected motion of atarget volume exceeds a predetermined motion threshold during treatment,the treatment beam is typically shut off (gated) to prevent violation ofthe dosimetric constraints for non-target tissue. As a result, theduration of the breath-hold-based portion of a treatment fraction isextended, which can be uncomfortable for a patient, or even exceed theability of the patient to remain motionless. Accordingly, there is aneed in the art for improved systems and techniques for beam-off motionthresholds in radiation therapy.

According to various embodiments, beam-off motion thresholds are basedon one or more dosimetrically determined treatment breath-hold levelsfor a particular patient. Beam-off motion thresholds determined asdescribed herein are a better indicator of the dosimetric consequencesof patient motion that is detected during radiation treatment thanconventional beam-off motion thresholds, which are based on externalmeasurements not precisely representing the motion of internalanatomical structures. Therefore, the herein-described beam-off motionthresholds for a target region can provide sufficient margin around aplanned treatment location for the target region to limit significantmisalignment between treatment fields and non-target tissue withoutimposing overly strict beam-off conditions that result in frequent beamholds during radiation treatment. Thus, the trade-off between dosedelivered to the target volume and dose received by critical anatomicalstructures is minimized or otherwise reduced. Further, in someembodiments, dynamic beam-off thresholds are employed that are modifiedduring a portion of a treatment fraction based on dose acquired innon-target tissue during that portion of the treatment fraction. Forexample, in such embodiments, as a dose budget for non-target tissue isexpended during a breath-hold-based portion of a treatment fraction, abeam-off motion threshold is reduced, so that later in the samebreath-hold-based portion of the treatment fraction, less motion of thetarget volume relative to the planned treatment location may cause abeam hold to occur. In such embodiments, motion of the target volumeaway from the planned treatment location generally does not result in abeam hold until a dose budget for the non-target tissue is exceeded. Asa result, a brief excursion of the target volume away from the plannedtreatment location usually does not result in a beam hold, and theduration of that breath-hold-based portion of the treatment fraction isnot increased.

FIG. 1 is a perspective view of a radiation therapy system 100 that canbeneficially implement various aspects of the present disclosure.Radiation therapy (RT) system 100 is a radiation system configured todetect intra-fraction motion in near-real time using X-ray imagingtechniques. Thus, RT system 100 is configured to provide stereotacticradiosurgery and precision radiotherapy for lesions, tumors, andconditions anywhere in the body where radiation treatment is indicated.As such, RT system 100 can include one or more of a linear accelerator(LINAC) that generates a megavolt (MV) treatment beam of high energyX-rays, one or more kilovolt (kV) X-ray sources, one or more X-rayimagers, and, in some embodiments, an MV electronic portal imagingdevice (EPID). By way of example, radiation therapy system 100 isdescribed herein configured with a circular gantry. In otherembodiments, radiation therapy system 100 can be configured with aC-gantry capable of infinite rotation via a slip ring connection or aC-arm configured with cable wind-up. Further, in some embodiments, RTsystem 100 is configured to generate a treatment beam of proton and/orother heavy charged particles in addition to or in lieu of an X-raytreatment beam. In some embodiments RT system 100 may be any externalbeam radiation delivery system known in the art or available on themarket.

Generally, RT system 100 is capable of kV imaging of a target volumeimmediately prior to or during application of an MV treatment beam, sothat an IGRT and/or an intensity-modulated radiation therapy (IMRT)process can be performed using X-ray imaging. RT system 100 may includeone or more touchscreens 101, couch motion controls 102, a bore 103, abase positioning assembly 105, a couch 107 disposed on base positioningassembly 105, and an image acquisition and treatment control computer106, all of which are disposed within a treatment room. RT system 100further includes a remote control console 110, which is disposed outsidethe treatment room and enables treatment delivery and patient monitoringfrom a remote location. Base positioning assembly 105 is configured toprecisely position couch 107 with respect to bore 103, and motioncontrols 102 include input devices, such as button and/or switches, thatenable a user to operate base positioning assembly 105 to automaticallyand precisely position couch 107 to a predetermined location withrespect to bore 103. Motion controls 102 also enable a user to manuallyposition couch 107 to a predetermined location.

In some embodiments, RT system 100 further includes one or morepatient-monitoring optical sensors 109 disposed proximate couch 107. Insome embodiments, one or more of optical sensors 109 are mounted on anend of couch 107 opposite bore 103. Alternatively or additionally,patient-monitoring optical sensors 109 may be disposed proximate bore103 and/or in a treatment room containing RT system 100.Patient-monitoring optical sensors 109 are configured as a patientposition-monitoring system that generates an external motion signalindicating a specific magnitude of respiratory motion by a patient oncouch 107. Thus, patient-monitoring optical sensors 109 can obtain amotion trace of one or more points on a surface of the body of thepatients, for example based on the motion of a fiducial or otherexternal marker (or markers) that is/are positioned to movesynchronously with a target volume of the patient. In another example,in some embodiments, patient-monitoring optical sensors 109 areconfigured to monitor respiratory motion via surface measurement basedon optical processing of a markerless surface of the body of thepatient. In some embodiments, a motion trace obtained bypatient-monitoring sensors 109 can be correlated to specific internalmotion of anatomical structures of the patient that is detected viaX-ray imaging, magnetic resonance imaging (MRI), and/or the like. Insome embodiments, patient-monitoring optical sensors 109 include one ormore cameras, surface scanners, and the like.

FIG. 2 schematically illustrates a drive stand 200 and gantry 210 of RTsystem 100, according to various embodiments. Covers, base positioningassembly 105, couch 107, and other components of RT system 100 areomitted in FIG. 2 for clarity. Drive stand 200 is a fixed supportstructure for components of RT treatment system 110, including gantry210 and a drive system 201 for rotatably moving gantry 210. Drive stand200 rests on and/or is fixed to a support surface that is external to RTtreatment system 110, such as a floor of an RT treatment facility.Gantry 210 is rotationally coupled to drive stand 200 and is a supportstructure on which various components of RT system 100 are mounted,including a linear accelerator (LINAC) 204, an MV electronic portalimaging device (EPID) 205, an imaging X-ray source 206, and an X-rayimager 207. During operation of RT treatment system 110, gantry 220rotates about bore 103 when actuated by drive system 201.

Drive system 201 rotationally actuates gantry 210. In some embodiments,drive system 201 includes a linear motor that can be fixed to drivestand 200 and interacts with a magnetic track (not shown) mounted ongantry 210. In other embodiments, drive system 201 includes anothersuitable drive mechanism for precisely rotating gantry 210 about bore201. LINAC 204 generates an MV treatment beam 230 of high energy X-rays(or in some embodiments electrons, protons, and/or other heavy chargedparticles, ultra-high dose rate X-rays (e.g., for FLASH radiotherapy) ormicrobeams for microbeam radiation therapy) and EPID 205 is configuredto acquire X-ray images with treatment beam 230. Imaging X-ray source206 is configured to direct a conical beam of X-rays, referred to hereinas imaging X-rays 231, through an isocenter 203 of RT system 100 toX-ray imager 207, and isocenter 203 typically corresponds to thelocation of a target volume 209 to be treated. In the embodimentillustrated in FIG. 2 , X-ray imager 207 is depicted as a planar device,whereas in other embodiments, X-ray imager 207 can have a curvedconfiguration. The embodiment of drive system 201 depicted in FIG. 2 isprovided as an example configuration. In other embodiments, such asembodiments in which MV treatment beam 230 includes heavy chargedparticles and/or ultra-high dose rate X-rays, drive system 201 may havea substantially different configuration than that shown in FIG. 2 .

X-ray imager 207 receives imaging X-rays 231 and generates suitableprojection images therefrom. According to certain embodiments, suchprojection images can then be employed to construct or update portionsof imaging data for a digital volume that corresponds to athree-dimensional (3D) region that includes target volume 209. That is,a 3D image of such a 3D region is reconstructed from the projectionimages. In some embodiments, cone-beam computed tomography (CBCT) and/ordigital tomosynthesis (DTS) can be used to process the projection imagesgenerated by X-ray imager 207. CBCT is typically employed to acquireprojection images over a relatively long acquisition arc, for exampleover a rotation of 180° or more of gantry 210. As a result, ahigh-quality 3D reconstruction of the imaged volume can be generated.CBCT is often employed at the beginning of a radiation therapy sessionto generate a set-up 3D reconstruction. For example, CBCT may beemployed immediately prior to application of treatment beam 230 togenerate a 3D reconstruction confirming that target volume 209 has notmoved or changed shape. Alternatively, or additionally, in someembodiments, partial-data reconstruction is performed by RT system 100during portions of an IGRT or IMRT process in which partial image datais employed to generate a 3D reconstruction of target volume 209. Forexample, as treatment beam 230 is directed to isocenter 203 while gantry210 rotates through a treatment arc, DTS image acquisitions can beperformed to generate image data for target volume 209. Because DTSimage acquisition is performed over a relatively short acquisition arc,for example between about 10° and 60°, near real-time feedback for theshape and position of target volume 209 can be provided by DTS imagingduring the IGRT process.

In the embodiment illustrated in FIG. 2 , RT system 100 includes asingle X-ray imager and a single corresponding imaging X-ray source. Inother embodiments, RT system 100 can include two or more X-ray imagers,each with a corresponding imaging X-ray source. One such embodiment isillustrated in FIG. 3 .

FIG. 3 schematically illustrates a drive stand 300 and gantry 310 of RTsystem 100, according to various embodiments. Drive stand 300 and gantry310 are substantially similar in configuration to drive stand 200 andgantry 200 in FIG. 2 , except that the components of RT system 100 thatare mounted on gantry 310 include a first imaging X-ray source 306, afirst X-ray imager 307, a second imaging X-ray source 308, and a secondX-ray imager 309. In such embodiments, the inclusion of multiple X-rayimagers in RT system 100 facilitates the generation of projection images(for reconstructing the target volume) over a shorter image acquisitionarc. For instance, when RT system 100 includes two X-ray imagers andcorresponding X-ray sources, an image acquisition arc for acquiringprojection images of a certain image quality can be approximately halfthat for acquiring projection images of a similar image quality with asingle X-ray imager and X-ray source.

The projection images generated by X-ray imager 207 (or by first x-rayimager 307 and second X-ray imager 309) are used to construct imagingdata for a digital volume of patient anatomy within a 3D region thatincludes the target volume. Alternatively or additionally, suchprojection images can be used to update portions of an existing imagingdata for the digital volume corresponding to the 3D region. Oneembodiment of such a digital volume is described below in conjunctionwith FIG. 4 .

FIG. 4 schematically illustrates a digital volume 400 that isconstructed based on projection images generated by one or more X-rayimagers included in RT system 100, according to various embodiments. Forexample, in some embodiments, the projection images can be generated bya single X-ray imager, such as X-ray imager 207, and in otherembodiments the projection images can be generated by multiple X-rayimagers, such as first x-ray imager 307 and second X-ray imager 309.

Digital volume 400 includes a plurality of voxels 401 (dashed lines) ofanatomical image data, where each voxel 401 corresponds to a differentlocation within digital volume 400. For clarity, only a single voxel 401is shown in FIG. 4 . Digital volume 400 corresponds to a 3D region thatincludes target volume 410. In FIG. 4 , digital volume 400 is depictedas an 8×8×8 voxel cube, but in practice, digital volume 400 generallyincludes many more voxels, for example orders of magnitude more than areshown in FIG. 4 .

For purposes of discussion, target volume 410 can refer to the grosstumor volume (GTV), clinical target volume (CTV), or the planning targetvolume (PTV) for a particular treatment. The GTV depicts the positionand extent of the gross tumor, for example what can be seen or imaged;the CTV includes the GTV and an additional margin for sub-clinicaldisease spread, which is generally not imagable; and the PTV is ageometric concept designed to ensure that a suitable radiotherapy doseis actually delivered to the CTV without adversely affecting nearbyorgans at risk. Thus, the PTV is generally larger than the CTV, but insome situations can also be reduced in some portions to provide a safetymargin around an organ at risk. The PTV is typically determined based onimaging performed prior to the time of treatment, and alignment of thePTV with the current position of patient anatomy at the time oftreatment is facilitated by X-ray imaging of digital volume 400.

According to various embodiments described below, image informationassociated with each voxel 401 of digital volume 400 is constructed viaprojection images generated by the single or multiple X-ray imagers viaa CBCT process. For example, such a CBCT process can be employedimmediately prior to delivering treatment beam 230 to target volume 410,so that the location and shape of target volume 410 can be confirmedbefore treatment begins. In addition, according to various embodimentsdescribed below, image information associated with some or all of voxels401 of digital volume 400 is updated via projection images generated bythe single or multiple X-ray imagers via a DTS process. For example,such a DTS process can be employed after a portion of a plannedtreatment has begun and before the planned treatment has completed. Inthis way, the location and shape of target volume 410 can be confirmedwhile the treatment is underway. Thus, if a sufficient portion of thetarget volume 410 is detected to be extending outside a thresholdregion, the treatment can either be aborted or modified. In such aninstance, modification of the treatment can be accomplished by adjustingpatient position and/or the treatment beam.

According to various embodiments, a radiation therapy process includesdetermining a specific breath-hold level (referred to herein as a“treatment breath-hold level”) and employing the treatment breath-holdlevel during radiation therapy. The treatment breath-hold level isdetermined based on one or more dosimetric plan properties of atreatment plan, such as target coverage, organ-at risk (OAR) dose volumeparameters, geometric parameters, and the like. The radiation therapyprocess further includes determining and employing beam-off thresholdsfor allowable movement of a target volume during the radiation therapy.The beam-off thresholds are based on a dosimetric analysis of thetreatment breath-hold level and one or more breath-hold levels that areadjacent or proximate to the treatment breath-hold level. One suchembodiment is described below in conjunction with FIG. 5 .

FIG. 5 is a block diagram illustrating a breath-hold-based radiationtherapy process 500, according to various embodiments. In the embodimentillustrated in FIG. 5 , breath-hold-based radiation therapy process 500includes a patient training phase 501, a dosimetric analysis phase 502,and a radiation therapy phase 503.

In patient training phase 501, suitability of a particular patient fortreatment via breath-hold-based radiation therapy process 500 isdetermined and the patient is educated and trained for the breath-holdprocedures to be employed in dosimetric analysis phase 502 and radiationtherapy phase 503. For example, in some embodiments, the capability ofthe patient is evaluated in a pre-image acquisition session forperforming a breath hold at a level and for a duration that iscompatible with the breath-hold based treatment included inbreath-hold-based radiation therapy process 500. In the embodiments, thepatient is trained to perform various breath-hold levels, where eachbreath-hold level corresponds to a unique volume of breath being held.It is noted that, for each breath-hold level, there is an associatedconfiguration of the anatomical positions of internal structures. Aspart of the training process, the patient performs various breath-holdlengths and breath-hold repetitions to confirm that the patient cancomply with the boundary conditions of the breath-hold based treatmentincluded in breath-hold-based radiation therapy process 500. Successfulcompletion of patient training phase 501 ensures that the patient iscapable of undergoing CT image acquisition and the various breath-holdlevels that occur in dosimetric analysis phase 502 and radiation therapyphase 503.

In some embodiments, in addition to static breath-hold training, apatient is trained in regular free-breathing that encompasses certaintargeted breath-hold levels in patient training phase 501. Suchsupplemental training enables free-breathing-based approaches that canbe employed as part of dosimetric analysis phase 502.

Various conventional techniques can be employed in patient trainingphase 501 to facilitate the breath-hold procedures of patient trainingphase 501. In some embodiments, audio-visual breath-hold guidance can beemployed in patient training phase 501. Alternatively or additionally,intercostal muscle training and/or other breathing training can beemployed in patient training phase 501 to improve breath-hold length orto guide breath-hold level and length. Alternatively or additionally, amechanical ventilator can be employed in patient training phase 501 toimprove breath-hold length or to guide breath-hold level and length.

In dosimetric analysis phase 502, a treatment breath-hold level for thepatient is determined that causes a beneficial anatomical configurationof patient internal structures for radiation therapy. For example, abreath-hold level that is demonstrated to position a target volume awayfrom a critical anatomical structure (such as an OAR) is a breath-holdlevel that may be selected as the treatment breath-hold level for thepatient. In addition, beam-off motion thresholds are also determined indosimetric analysis phase 502. Such beam-off motion thresholds indicateallowable movement of a target volume during radiation therapy phase503. One embodiment of dosimetric analysis phase 502 is described belowin conjunction with FIG. 6 .

In radiation therapy phase 503, a treatment plan is implemented on thepatient using the treatment threshold level and the beam-off motionthresholds determined in dosimetric analysis phase 502. Generally,radiation therapy phase 503 includes multiple treatment fractions, eachof which may include a single or multiple breath-hold-based portionsthat each occur over a single breath hold. In some embodiments,radiation therapy phase 503 may include a single treatment fraction.Radiation therapy phase 503 is described below in conjunction with FIG.11 .

FIG. 6 sets forth a flowchart of dosimetric analysis phase 502,according to one or more embodiments. As noted above, dosimetricanalysis phase 502 includes a process for determining a treatmentbreath-hold level for a patient and for generating beam-off thresholdsfor allowable movement of a target volume during breath-hold-basedradiation treatment of the patient. Dosimetric analysis phase 502 mayinclude one or more operations, functions, or actions as illustrated byone or more of blocks 601-620. Although the blocks are illustrated in asequential order, these blocks may be performed in parallel, and/or in adifferent order than those described herein. Also, the various blocksmay be combined into fewer blocks, divided into additional blocks,and/or eliminated based upon the desired implementation. Althoughdosimetric analysis phase 502 is described in conjunction with thesystems of FIGS. 1-4 , persons skilled in the art will understand thatany suitably configured radiation therapy system is within the scope ofthe present embodiments.

In step 601, a computing device causes imaging of the anatomy of apatient to be performed, such as treatment control computer 106 and/orremote control console 110 of FIG. 1 , or any other suitable computingdevice. Specifically, for various breath-hold levels, athree-dimensional (3D) image is acquired and a corresponding breath-holdcurve or other external motion signal is measured. Based on the 3Dimages and the breath-hold curves, a correlation between an externalmotion signal and a current position of a target volume and/or otherinternal anatomy can be established. Thus, during radiation treatment,measurement of the external motion signal can indicate the currentposition of the target volume without the use of X-ray or MRI imaging.In an alternative embodiment, no breath-hold curve is measured in step601, and 3D imaging during treatment is employed to determine thecurrent position of a target volume during the treatment.

In some embodiments, the 3D imaging performed in step 601 includes MRIimaging of an anatomical region surrounding a target volume.Alternatively or additionally, in some embodiments, the 3D imagingperformed in step 601 includes X-ray imaging of the anatomical region,such as CBCT imaging and/or 4D-CT imaging. In 4D-CT, multiple phases(e.g., five to ten) of motion in the anatomical region is imaged. Insuch embodiments, the 4D-CT imaging may be performed in conjunction withtrained and/or assisted free-breathing by the patient. In someembodiments, during the 3D imaging, audio-visual breath-hold guidance, amechanical ventilator, and/or any other suitable technique can beemployed to improve breath-hold length or to guide breath-hold level andlength.

In some embodiments, the measurement of the external motion signalperformed in step 601 includes obtaining a motion trace of a point orpoints on the surface of the body of the patient. For example, in someembodiments, the measurement of the external motion signal is performedvia patient-monitoring optical sensors 109 and one or more fiducials,other markers, and/or position sensor(s). Thus, in such embodiments,motion associated with the respiration cycle of the patient is measuredin conjunction with the above-described 3D imaging of the anatomicalregion surrounding the target volume. Generally, the location orlocations of the fiducials, markers, and/or position sensors areselected so that said fiducials, markers, and/or position sensors movesynchronously, or substantially synchronously, with the target volume ofthe patient.

In step 602, for each breath-hold level to be considered duringdosimetric analysis phase 502, the computing device: generates a 3Dmodel of the patient anatomy surrounding the target volume; determines avalue for target position that indicates motion of the target volume atthe breath-hold level; determines a specific value of the externalmotion signal that is associated with the breath-hold level; andcorrelates the specific value of the external motion signal with thevalue for target position. As a result of the correlation, targetposition can be inferred during a radiation treatment based on ameasurement of the external motion signal.

Generally, the computing device generates each 3D model of the patientanatomy in step 602 based on a CT data set or MRI data set generated instep 601. In addition, in step 602 the computing device determines thevalue for target position for a breath-hold level via the 3D model forthat breath-hold level. The target position value may indicate aposition of a target volume, a position of a specific portion of atarget volume (e.g., an edge region of the target volume or a centerpoint of the target volume), a position of an OAR, a position of aspecific portion of the OAR (e.g., an edge region of the OAR or a centerpoint of an OAR), and the like. Such positions may be measured relativeto any suitable datum location within or proximate to the anatomy of thepatient. Further, in step 602 the computing device determines thespecific value of the external motion signal for each breath-hold levelvia a different breath-hold curve, where each different breath-holdcurve indicates the external motion signal for a particular breath hold.One embodiment of a breath-hold curve is described below in conjunctionwith FIG. 7 .

FIG. 7 is an illustration of a breath-hold curve 700, according tovarious embodiments. Breath-hold curve 700 shows variations in externalmotion signal 705 over a time interval 701 that includes a patientbreath hold, such as a patient breath hold performed during patienttraining phase 501, step 601 of dosimetric analysis phase 502, orradiation therapy phase 503. As described above, external motion signal705 indicates a position of a point or points on the surface of the bodyof the patient, such as one or more fiducials, other markers, and/orposition sensor(s). Such positions may be measured relative to anysuitable datum location within or proximate to the anatomy of thepatient.

As shown, the exact value of external motion signal 705 generally variesover time, even when the patient successfully maintains a breath holdthroughout time interval 701. Also shown in FIG. 7 is an imaginginterval 702 (cross-hatched), during which the 3D imaging of step 601takes place. In some embodiments, the specific value of the externalmotion signal that is associated with breath-hold curve 700 isdetermined based at least in part on the 3D imaging of step 601. In suchembodiments, the specific value of the external motion signal that isassociated with breath-hold curve 700 may be based on some or all of theportion of breath-hold curve 700 that is disposed within imaginginterval 702. For example, in one such embodiment, the specific value ofthe external motion signal associated with breath-hold curve 700 isbased on an average value 703 of external motion signal 705 disposedwithin imaging interval 702. Thus, in such embodiments, the specificvalue of the external motion signal associated with breath-hold curve700 (e.g., average value 703) can be correlated, via the above-described3D imaging, to a specific configuration of the anatomical regionsurrounding the target volume that is imaged during imaging interval702. As a result, an external motion signal measured during subsequentradiation therapy indicates target motion, as described below inconjunction with FIG. 8 .

FIG. 8 is an illustration of a breath-hold correlation curve 800,according to various embodiments. Breath-hold correlation curve 800shows variations in target position 805 over a time interval 801 thatincludes a patient breath hold, such as a patient breath hold performedduring radiation therapy phase 503. Target position 805 indicates aposition of a target associated with a target volume or OAR. In someembodiments, target position 805 is not measured directly, and insteadis determined by a computing device based on an external motion signalthat is correlated to target position 805. Alternatively, in someembodiments, target position 805 is based at least in part on 3D imagingof the anatomical region surrounding the target volume, other 2D X-rayimaging, and/or digital tomosynthesis (DTS) imaging. In suchembodiments, information included in such imaging can be employed tocorrect target position 805 during radiation therapy phase 503 for moreaccurate calculation of dose received by non-target tissue. In eithercase, breath-hold correlation curve 800 can be employed in conjunctionwith beam-off thresholds during radiation therapy phase 503, asdescribed below, to reduce dose received by non-target tissue withoutimposing overly strict beam-off conditions that result in frequent beamholds during radiation treatment.

Returning to FIG. 6 , in some embodiments, one or more interpolatedbreath-hold levels and associated 3D models are also generated in step602. For example, in an instance in which five 3D CT scans are performedfor five different breath-hold levels (e.g., breath-hold levels 1-5),one or more additional breath-hold levels are generated betweenbreath-hold levels 1 and 2 based on interpolation between thebreath-hold levels 1 and 2, and one or more additional 3D models aregenerated based on the 3D models associated with breath-hold levels 1and 2. Similarly, one or more additional breath-hold levels and 3Dmodels can be generated between breath-hold levels 2 and 3 and betweenbreath-hold levels 3 and 4. In such embodiments, interpolation between3D models can be performed based on deformable image registration ofacquired 3D information, such as acquired CT data.

In step 603, a treatment planning directive is received, for examplefrom a physician, such as a radiation oncologist, or from treatmentplanning software. The physician intent of the treatment is specified inthe treatment planning directive, and may include pre-defined dosevolume and/or geometric parameters, such as a minimum distance ofdose-limiting OARs and/or margins to be applied to such OARs.

The treatment planning directive may be generated based on some or allof the 3D models generated in step 602. The treatment planning directivetypically describes image studies for a treatment site, including targettissue structures and normal tissue structures to be defined via theimaging studies. These target and normal tissue structures aresubsequently used for treatment planning. For scoring multiple treatmentplans within an optimization process, the treatment planning directivemay also specify expansions of the target tissue structures and normaltissue structures. Thus, in addition to the gross tumor volume (GTV),the treatment planning directive may further include clinical targetvolume (CTV), the internal target volume (ITV), the planning targetvolume (PTV), OARs, and/or a planning organ at risk volume (PRV), amongothers. The treatment planning directive may further specify radiationtherapy prescription guidelines, planning suggestions, and/or specialinstructions.

In some instances, a radiation oncologist generates some or all of thetreatment planning directive, for example based on local clinicalstandards, specific medical conditions of the patient, and the like.Alternatively, in some instances, the radiation oncologist can beassisted by a software application configured to suggest some or all ofthe information included in the treatment planning directive.

In step 604, the computing device performs segmentation of eachbreath-hold level 3D model generated in step 602. For example, in someembodiments, for each 3D model, an auto segmentation of the OAR andtarget volume is performed. Alternatively, in some embodiments, thesegmentation for one or more of the 3D models is performed manually by aphysician.

In step 605, the computing device generates a treatment plan for eachbreath-hold level 3D model generated in step 602. Generally each suchtreatment plan is generated based at least in part on the physicianintent specified in the treatment planning directive. Each treatmentplan may include one or more beam geometries, a dose distribution foreach beam geometry, and the treatment fractions for implementing theplanned treatment.

In step 606, the computing device determines performance of each 3Dmodel and associated treatment plan. For example, in some embodiments,the computing device performs a dosing simulation for each 3D model andassociated treatment plan and compares the simulated dosing to the dosevolume and/or geometric parameters specified in the treatment planningdirective. In some embodiments, the dosing simulation for each 3D modeland associated treatment plan is performed assuming that no motion ofthe target volume occurs. In such embodiments, only non-motion marginsare applied to the target volume.

In step 607, the computing device determines beam-off thresholds for thebest-performing 3D model and associated treatment plan scored in step606. The beam-off thresholds indicate allowable movement of a targetvolume during breath-hold-based radiation treatment of the patient whenthe patient performs a breath-hold at the breath-hold level thatcorresponds to the best-performing 3D model (referred to herein as the“treatment breath-hold level”).

In some embodiments, the beam-off thresholds are determined in step 607by applying the treatment plan associated with the best-performing 3Dmodel to the one or more neighboring breath-hold levels. In this way,the dosing of non-target tissue that occurs during a treatment fractionwhen a patient involuntarily varies breath-hold level from the treatmentbreath-hold level to a neighboring breath-hold level can be estimated.In the embodiments, each beam-off threshold corresponds to a breath-holdlevel that is different from the treatment breath-hold level but stilldoes not result in violation of one or more dosing parameters specifiedin the treatment planning directive.

In some embodiments, the computing device determines static beam-offthresholds for the treatment plan, and in other embodiments, thecomputing device determines dynamic beam-off thresholds for thetreatment plan. An embodiment of static beam-off thresholds is describedbelow in conjunction with FIG. 9 , and an embodiment of dynamic beam-offthresholds is described below in conjunction with FIG. 10 .

FIG. 9 is an illustration of a breath-hold correlation curve 900 withstatic beam-off thresholds 920, according to various embodiments.Breath-hold correlation curve 900 is substantially similar tobreath-hold correlation curve 800 of FIG. 8 , and shows target position805 over time interval 801. As described above, in some embodimentstarget position 805 is not measured directly, and instead is determinedby a computing device based on an external motion signal that iscorrelated to target position 805. In addition, FIG. 9 shows staticbeam-off thresholds 920 and an ideal target position 905.

Ideal target position 905 indicates a desired position of a target(e.g., a target volume, a position of a specific portion of a targetvolume, a position of an OAR, a position of a specific portion of anOAR, etc.) during breath-hold-based radiation treatment of a patient. Insome embodiments, ideal target position 905 corresponds to the locationof the target when the patient correctly performs a breath hold at thetreatment breath-hold level for the patient. Thus, ideal target position905 corresponds to the breath-hold level that is determined to be thebreath-hold level that corresponds to the best-performing 3D modelgenerated in step 602.

Static beam-off threshold 920 indicates allowable movement of a targetduring breath-hold-based radiation treatment of the patient, where theallowable movement does not violate one or more dosimetric or geometricparameters of the treatment planning directive. Thus, when targetposition 805 is greater than an upper static beam-off threshold 921 orless than a lower static beam-off threshold 922 during radiationtreatment, a beam-hold occurs and the treatment beam is shut off.

FIG. 9 also shows beam-on times 930 (cross-hatched) that occur duringtime interval 801. As shown, beam-on times 930 occur during timeinterval 801 when target position 805 is within a range of beam-offthreshold positions for the target region. Thus, in the embodimentillustrated in FIG. 9 , beam-on times 930 occur when target position 805is less than upper static beam-off threshold 921 and greater than lowerstatic beam-off threshold 922.

In some embodiments, to avoid frequent beam-holds, beam-on times 930continue for a predetermined time interval after target position 805 isdetermined to be greater than upper static beam-off threshold 921 orless than lower static beam-off threshold 922. In such embodiments, thepredetermined time interval is generally short, for example less thanone second, and can be a user-defined value, a system-defined value, ora value based on dosimetric analysis of the current breath-hold-basedportion of a treatment fraction.

In some embodiments, breath-hold correlation curve 900 includes multipledose bins 940 that are adjacent or proximate to ideal target position905. In such embodiments, each dose bin corresponds to a range of targetpositions associated with a particular breath-hold level. Thus, in theembodiment illustrated in FIG. 9 , a dose bin 941 corresponds to targetpositions associated with a slightly lower breath-hold level than thatassociated with ideal target position 905, a dose bin 942 corresponds totarget positions associated with a slightly lower breath-hold level thanthat associated with dose bin 941, a dose bin 943 corresponds to targetpositions associated with a higher breath-hold level than thatassociated with ideal target position 905, and a dose bin 944corresponds to target positions associated with a slightly higherbreath-hold level than that associated with dose bin 943.

Dose bins 940 enable more accurate determination of dosing of non-targettissue during beam-on times 930. Further, in some embodiments, dose binsenable determination of dosing of specific regions of non-target tissueduring beam-on times 930. For example, in some embodiments, non-targettissue that receives higher dosing when target position 805 is disposedwithin dose bin 944 may differ from non-target tissue that receiveshigher dosing when target position 805 is disposed within dose bin 942.Thus, dose bins 940 enable more granular determination of dosing ofnon-target tissue during a breath-hold-based portion of a treatmentfraction.

In the embodiment illustrated in FIG. 9 , breath-hold correlation curve900 includes four dose bins 941-944, but in other embodiments,breath-hold correlation curve 900 can include more than or fewer thanfour dose bins 940. Further, in the embodiment illustrated in FIG. 9 ,dose bins 940 are symmetric in size and position relative to idealtarget position 905, but in other embodiments, dose bins 940 may eachrepresent different-sized ranges of target position 805.

FIG. 10 is an illustration of a breath-hold correlation curve 1000 withdynamic beam-off thresholds 1020, according to various embodiments.Breath-hold correlation curve 1000 is substantially similar tobreath-hold correlation curve 900 of FIG. 9 , and shows target position805 over time interval 801, ideal target position 905, and dose bins940. In addition, FIG. 10 shows dynamic beam-off thresholds 1020.

Dynamic beam-off thresholds 1020 enable dose monitoring during radiationtreatment that is based on which specific dose bin target position 805is located in and on the time during which target position 805 remainswithin that specific dose bin. The monitored dosing of non-target tissueproximate the target is then compared to a dose budget for suchnon-target tissue to determine whether a position of one or both dynamicbeam-off thresholds 1020 should be modified. In some embodiments, basedon the remaining dose budget and on the accumulated dose associated withthe current target position 805, a dynamic beam-off threshold 1020 maybe modified. For example, when a dosing of non-target tissue associatedwith dose bin 944 is determined to have exceeded (or alternatively ispredicted to exceed) a dose budget for the non-target tissue, dynamicbeam-off threshold 1021 is moved from a boundary of dose bin 944 to aboundary of dose bin 943, as indicated by arrow 1049. Thus, in suchembodiments, a dynamic beam-off threshold 1020 is modified byassociating the position of the dynamic beam-off threshold 1020 with afirst range of target positions (e.g., the target positions representedby dose bin 943) and disassociating the position of the dynamic beam-offthreshold 1020 from a second range of target positions (e.g., the targetpositions represented by dose bin 944).

In some embodiments, monitoring the dosing of non-target tissue is basedon the dose bin 940 in which current target position 805 is disposed andon a current beam (or beamlet) intensity. Thus, in such embodiments,during a specific time interval, the dosing of non-target tissue is afunction of the duration of the specific time interval, the planned beamintensity, and the particular dose bin in which current target position805 is disposed. By way of example, FIG. 10 includes a beam intensityplot 1050 showing the different levels of beam intensity planned tooccur during time interval 801.

Returning to FIG. 6 , in step 608, the computing device determineswhether the (static or dynamic) beam-off thresholds meet physicianintent and/or other goals included in the treatment planning directive.For example, in some embodiments, the computing device determineswhether a particular beam-off threshold meets goals included in thetreatment planning directive by simulating application of the treatmentplan associated with the best-performing 3D model generated in step 605while the target position 805 is at that particular beam-off threshold.When such simulation indicates that the particular beam-off thresholdfails to meet one or more goals included in the treatment planningdirective, and the particular beam-off threshold is based on abreath-hold level that is adjacent to the treatment breath-hold level,there is little or no beam-off threshold available. Consequently, use ofthe treatment breath-hold level and the associated treatment plan willgenerally result in frequent beam holds. In such an instance, the goalsof the treatment planning directive and patient anatomy are notcompatible, and modification of the treatment planning directive isrequested. Thus, when the computing device determines in step 608 thatone or more beam-off thresholds fail to meet one or more goals includedin the treatment planning directive, dosimetric analysis phase 502proceeds to step 611; when the computing device determines the beam-offthresholds meet all goals included in the treatment planning directive,dosimetric analysis phase 502 proceeds to step 613.

In step 611, the computing device requests one or more modifications tothe treatment planning directive and/or generates a notification/warningthat the treatment planning directive requires modification.

In step 612, the computing device receives a modified treatment planningdirective. In some instances, the treatment planning directive ismodified by a physician and in other instance by treatment planningsoftware. In some instances, the modified treatment planning directiveincludes modified dose volume and/or geometric parameters thatfacilitate non-zero beam-off thresholds for the anatomical structuresand target volume location of the current patient. In some instances,the modified treatment planning directive includes an escalated tumordose and/or geometric parameters that result in a tighter doseparameter.

In step 613, the computing device determines whether the beam-offthresholds determined in step 607 are too large. For example, in someembodiments, such a determination is made based on an absolute maximumthreshold value (e.g., 5 mm), a maximum threshold value relative to adose volume and/or geometric parameter included in the treatmentplanning directive, and/or a value based on a dosimetric analysis of thecurrent breath-hold-based portion of a treatment fraction. When thecomputing device determines that one or more beam-off thresholds are toolarge, dosimetric analysis phase 502 proceeds to step 611; when thecomputing device determines that none of the beam-off thresholds are toolarge, dosimetric analysis phase 502 proceeds to step 620.

In step 620, the computing device finalizes the treatment planassociated with the best-performing 3D model generated in step 605.

FIG. 11 sets forth a flowchart of a treatment fraction process 1100 ofradiation therapy phase 503, according to one or more embodiments. Asnoted above, radiation therapy phase 503 generally includes multipletreatment fractions, each of which may include a single or multiplebreath-hold-based portions that each occur over a single breath hold. Intreatment fraction process 1100, a portion of the treatment plangenerated in dosimetric analysis phase 502 is implemented in conjunctionwith static beam-off thresholds or dynamic beam-off thresholds. In someembodiments, treatment fraction process 1100 is performed over a singlerotational arc of a gantry of radiation therapy system. Alternatively,in some embodiments, treatment fraction process 1100 is performed overmultiple rotational arcs of a gantry of a radiation therapy system.Alternatively, in some embodiments, treatment fraction process 1100 isperformed over a fraction of a rotational arc of a gantry of a radiationtherapy system or over multiple separate fractions of a rotational arcof the gantry. Alternatively, in some embodiments, treatment fractionprocess 1100 is performed in a static-gantry radiation therapy process,such as an IMRT or a 3D conformal radiation therapy process. Treatmentfraction process 1100 may include one or more operations, functions, oractions as illustrated by one or more of blocks 1101-1151. Although theblocks are illustrated in a sequential order, these blocks may beperformed in parallel, and/or in a different order than those describedherein. Also, the various blocks may be combined into fewer blocks,divided into additional blocks, and/or eliminated based upon the desiredimplementation. Although treatment fraction process 1100 is described inconjunction with the systems of FIGS. 1-10 , persons skilled in the artwill understand that any suitably configured radiation therapy system iswithin the scope of the present embodiments.

In step 1101, a radiation therapy system begins implementation of thecurrent breath-hold-based portion of a treatment fraction. In step 1102,the radiation therapy system determines the current target position 805.In some embodiments, current target position 805 is determined based onan external motion signal. Additionally, in some embodiments, thedetermination of current target position 805 is further based on 3Dimaging of the anatomical region surrounding a target volume of thepatient. In such embodiments, the 3D imaging (e.g., a 3D CT scan) isemployed to periodically correct the target position 805 indicated bythe external motion signal.

In step 1103, the radiation therapy system determines whether thecurrent target position 805 is within the beam-off thresholds generatedfor treatment fraction process 1100. If yes, treatment fraction process1100 proceeds to step 1131; if no, treatment fraction process 1100proceeds to step 1121. In step 1121, radiation therapy system performs abeam hold and shuts off the one or more treatment beams to be applied tothe target volume for a predetermined time interval. Alternatively, insome embodiments, compensatory couch motion is employed to preventtarget position 805 from moving outside the beam-off thresholds andthereby avoid a beam hold.

In step 1131, the radiation therapy system determines an accumulateddose that will occur if a treatment beam is applied to the target volumebased on the current target position 805. As noted above, theaccumulated dose may be based on the particular dose bin in whichcurrent target position 805 is disposed, the duration of the timeinterval during which the treatment beam is applied while targetposition 805 is disposed within the particular dose bin, and/or the beamintensity of the treatment beam while target position 805 is disposedwithin the particular dose bin.

In step 1132, the radiation therapy system determines whether theaccumulated dose determined in step 1131 is less than a current dosebudget. In some embodiments, the dose budget is associated with allnon-target tissue proximate the target volume. In other embodiments, thedose budget is associated with a specific anatomical structure and/orother critical structure or tissue type that is proximate the targetvolume. When the radiation therapy system determines that theaccumulated dose determined in step 1131 is less than the current dosebudget, treatment fraction process 1100 proceeds to step 1141; when theradiation therapy system determines that the accumulated dose determinedin step 1131 is greater than the current dose budget, treatment fractionprocess 1100 proceeds to step 1133.

In step 1133, the radiation therapy system determines a remaining dosebudget for non-target tissue, where the remaining dose budget is lessthan the current dose budget. According to various embodiments, a lowerdose budget generally results in stricter beam-off thresholds, asdescribed below. In general, a lower dose budget (such as the remainingdose budget determined in step 1133) results in stricter beam-offthresholds because a treatment beam can no longer be safely appliedwhile target position 805 is located in dose bins that are farther fromideal target position 905.

In step 1134, the radiation therapy system modifies one or more beam-offthresholds based on the remaining dose budget determined in step 1133.For example, in some embodiments, dynamic beam-off threshold 1021 ismoved from a boundary of one dose bin (e.g., dose bin 944) to a boundaryof a different dose bin that is closer to ideal target position 905(e.g., dose bin 943) in response to the remaining dose budget determinedin step 1133.

In step 1141, the radiation therapy system reduces the accumulatedbudget by the accumulated dose determined in step 1131. In step 1142,the radiation therapy system applies the treatment beam or beams to thetarget volume for a predetermined time interval, for example until a newtarget position 805 can be determined.

In step 1143, the radiation therapy system determines whether thecurrent breath-hold-based portion of a treatment fraction has beencompleted. If no, treatment fraction process 1100 returns to step 1102,and radiation therapy system continues the treatment fraction; if yes,treatment fraction process 1100 proceeds to step 1151, and radiationtherapy system ends the current breath-hold-based portion of a treatmentfraction. Treatment fraction process 1100 can then be employed toimplement a subsequent breath-hold-based portion of the treatmentfraction.

Treatment fraction process 1100 can be advantageously employed instereotactic and/or hypofractionation treatments, in which relativelyfew treatment fractions (e.g., five or ten) are performed and excursionsof target position 805 can have more serious effects. However, any othertechnically feasible radiation therapy process can benefit from theembodiments described herein, including techniques that include largernumbers of fractions (e.g., 20 or more).

In the embodiment of treatment fraction process 1100 described above,operations are performed with respect to a single dose budget, such as,for example, a dose budget associated with all non-target tissueproximate the target volume. In other embodiments, treatment fractionprocess 1100 can be performed with respect to multiple dose budgets. Forexample, in one such embodiment, a different dose budget is associatedwith and tracked for each different dose bin 940 of a breath-holdcorrelation curve employed in treatment fraction process 1100. Thus, insuch an embodiment, in step 1131 the radiation therapy system maydetermine the accumulated dose for the current dose bin 940 in whichtarget position 806 is located, and in step 1131 the radiation therapysystem may determine whether the accumulated dose determined in step1131 is less than a current dose budget for the current dose bin 940. Asa result, in such embodiments, the multiple dose budgets are trackedseparately for each does bin 940.

FIG. 12 is an illustration of computing device 1200 configured toperform various embodiments of the present disclosure. Computing device1200 may be a desktop computer, a laptop computer, a smart phone, or anyother type of computing device suitable for practicing one or moreembodiments of the present disclosure. In operation, computing device1200 is configured to execute instructions associated with patienttraining phase 501, dosimetric analysis phase 502, and/or treatmentfraction process 1100 as described herein. It is noted that thecomputing device described herein is illustrative and that any othertechnically feasible configurations fall within the scope of the presentdisclosure.

As shown, computing device 1200 includes, without limitation, aninterconnect (bus) 1240 that connects a processing unit 1250, aninput/output (I/O) device interface 1260 coupled to input/output (I/O)devices 1280, memory 1210, a storage 1230, and a network interface 1270.Processing unit 1250 may be any suitable processor implemented as acentral processing unit (CPU), a graphics processing unit (GPU), anapplication-specific integrated circuit (ASIC), a field programmablegate array (FPGA), any other type of processing unit, or a combinationof different processing units, such as a CPU configured to operate inconjunction with a GPU or digital signal processor (DSP). In general,processing unit 1250 may be any technically feasible hardware unitcapable of processing data and/or executing software applications,including patient training phase 501, dosimetric analysis phase 502,and/or treatment fraction process 1100.

I/O devices 1280 may include devices capable of providing input, such asa keyboard, a mouse, a touch-sensitive screen, and so forth, as well asdevices capable of providing output, such as a display device and thelike. Additionally, I/O devices 1280 may include devices capable of bothreceiving input and providing output, such as a touchscreen, a universalserial bus (USB) port, and so forth. I/O devices 1280 may be configuredto receive various types of input from an end-user of computing device1200, and to also provide various types of output to the end-user ofcomputing device 1200, such as displayed digital images or digitalvideos. In some embodiments, one or more of I/O devices 1280 areconfigured to couple computing device 1200 to a network.

Memory 1210 may include a random access memory (RAM) module, a flashmemory unit, or any other type of memory unit or combination thereof.Processing unit 1250, I/O device interface 1260, and network interface1270 are configured to read data from and write data to memory 1210.Memory 1210 includes various software programs that can be executed byprocessor 1250 and application data associated with said softwareprograms, including patient training phase 501, dosimetric analysisphase 502, and/or treatment fraction process 1100.

FIG. 13 is a block diagram of an illustrative embodiment of a computerprogram product 1300 for implementing a method for segmenting an image,according to one or more embodiments of the present disclosure. Computerprogram product 1300 may include a signal bearing medium 1304. Signalbearing medium 1304 may include one or more sets of executableinstructions 1302 that, when executed by, for example, a processor of acomputing device, may provide at least the functionality described abovewith respect to FIGS. 1-12 .

In some implementations, signal bearing medium 1304 may encompass anon-transitory computer readable medium 1308, such as, but not limitedto, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD),a digital tape, memory, etc. In some implementations, signal bearingmedium 1304 may encompass a recordable medium 1310, such as, but notlimited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In someimplementations, signal bearing medium 1304 may encompass acommunications medium 1306, such as, but not limited to, a digitaland/or an analog communication medium (e.g., a fiber optic cable, awaveguide, a wired communications link, a wireless communication link,etc.). Computer program product 1300 may be recorded on non-transitorycomputer readable medium 1308 or another similar recordable medium 1310.

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments.

Aspects of the present embodiments may be embodied as a system, methodor computer program product. Accordingly, aspects of the presentdisclosure may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.” Furthermore, aspects of the present disclosure maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

1. A computer-implemented method of performing a treatment fraction ofradiation therapy, the method comprising: determining a current positionof a target volume of patient anatomy; based on the current position ofthe target volume, computing an accumulated dose for tissue disposedwithin the target volume; determining that the accumulated dose is lessthan a current dose budget of the tissue; and in response to theaccumulated dose being less than the current dose budget, applying atreatment beam to the target volume while the target volume is in thecurrent position.
 2. The computer-implemented method of claim 1, whereinthe current position is at least partially outside a planned treatmentlocation for the target volume.
 3. The computer-implemented method ofclaim 1, further comprising generating a new value for the dose budgetby subtracting the accumulated dose from the current dose budget.
 4. Thecomputer-implemented method of claim 3, further comprising, based on thenew value of the dose budget, modifying a beam-off threshold positionfor the target volume.
 5. The computer-implemented method of claim 4,wherein modifying the beam-off threshold position for the target volumecomprises associating the beam-off threshold position with a first rangeof target positions and disassociating the beam-off threshold positionfrom a second range of target positions, wherein the first range oftarget positions is closer to a planned treatment location for thetarget volume than the second range of target positions.
 6. Thecomputer-implemented method of claim 1, further comprising, prior toapplying the treatment beam to the target volume, determining that thecurrent position is within a range of beam-off threshold positions forthe target volume.
 7. The computer-implemented method of claim 6,further comprising, when a detected position of the target volume isoutside the range of beam-off threshold positions, blocking applicationof the treatment beam for a portion of the treatment fraction.
 8. Thecomputer-implemented method of claim 1, further comprising: determiningan equivalent breath-hold level based on the current position of thetarget volume; and computing the accumulated dose based on theequivalent breath-hold level.
 9. The computer-implemented method ofclaim 8, wherein the equivalent breath-hold level is associated with aspecific accumulated dose.
 10. The computer-implemented method of claim1, further comprising: determining a treatment beam intensity that isapplied to the target volume while the target volume is in the currentposition; and computing the accumulated dose based on the treatment beamintensity.
 11. The computer-implemented method of claim 1, whereindetermining the current position of the target volume comprisesmeasuring an external motion signal.
 12. The computer-implemented methodof claim 1, wherein determining the current position of the targetvolume further comprises performing X-ray imaging of the target volume.13. The computer-implemented method of claim 1, further comprising basedon the current position of the target volume, computing an accumulateddose for the tissue.
 14. A system for performing a treatment fraction ofradiation therapy, the system comprising: an X-ray imaging device; atreatment-delivering X-ray source configured to direct treatment X-raysto a target volume of patient anatomy; an imaging X-ray sourceconfigured to direct imaging X-rays through the target volume and towardthe X-ray imager; and a processor configured to: determine a currentposition of the target volume; based on the current position of thetarget volume, compute an accumulated dose for tissue disposed withinthe target volume; determine that the accumulated dose is less than acurrent dose budget of the tissue; and in response to the accumulateddose being less than the current dose budget, cause thetreatment-delivering X-ray source to apply a treatment beam to thetarget volume while the target volume is in the current position. 15.The system of claim 14, wherein the current position is at leastpartially outside a planned treatment location for the target volume.16. The system of claim 14, wherein determining the current position ofthe target volume further comprises performing X-ray imaging of thetarget volume with the X-ray imaging device and the imaging X-raysource.
 17. The system of claim 14, wherein causing thetreatment-delivering X-ray source to apply the treatment beam to thetarget volume while the target volume is in the current positioncomprises a portion of the treatment fraction.
 18. Acomputer-implemented method of performing a treatment fraction ofradiation therapy, the method comprising: determining a current positionof a target volume of patient anatomy; based on the current position ofthe target volume, computing an accumulated dose for tissue associatedwith the target volume; determining that the accumulated dose is greaterthan a current dose budget of the tissue; and in response to theaccumulated dose being greater than the current dose budget: determininga remaining dose budget for the tissue associated with the targetvolume; and based on the remaining dose budget for the tissue, modifyinga beam-off threshold position for the target volume.
 19. The system ofclaim 18, wherein the tissue associated with the target volume comprisesone of tissue disposed within the target volume or non-target tissueproximate the target volume.
 20. The system of claim 19, furthercomprising: determining a new position of the target volume; based onthe new position of the target volume, computing a new accumulated dosefor the tissue; determining that the new accumulated dose is less thanthe remaining dose budget for the tissue; and in response to theaccumulated dose being less than the current dose budget, applying atreatment beam to the target volume while the target volume is in thenew position.